Monolithic and discrete microwave semiconductor devices are used for example to manufacture switches for microwave and millimeter wave applications. These switches may include PIN diodes as the active element. A PIN diode may be manufactured using the process taught in U.S. Pat. No. 5,268,310 owned by the assignee of the present invention, the disclosure of which is hereby specifically incorporated by reference. Electrical connection from a transmission line to the diode may be made through a wire bond that spans the mesa side wall of the PIN diode and electrically contacts the diode terminal. It is known that a diode connected in this way exhibits a resistive loss in the area of the access to the diode. It is also known that the loss at the bond is frequency related. Prior solutions to the lossy bond problem have been to increase the doping in the PIN mesa side wall. The increased doping reduces parasitic resistance and confines the carriers away from the side wall surface. Devices having the increased doping on the side walls, however, still exhibit significant loss. The exhibited loss also varies for devices in a single wafer, causing nonuniformity, as well as for devices on one wafer to the next, causing nonrepeatability. Variations in the operating parameters of semiconductor devices are detrimental to the effective use and application of these devices. Variations in predicted performance of the devices limit the design parameters for their application in that a circuit design must account for the expected variations in the performance parameters. It may or may not be possible to design the necessary tolerances into a circuit. If it is not possible for a product design to tolerate the expected variations in device or circuit performance, the product may not work that use those devices or circuits at the outer ends of the performance range.
There is a need, therefore, to reduce the loss associated with a discrete or monolithic semiconductor device in the area of the access to the device. There is a further need to improve the uniformity and repeatability of discrete and monolithic devices.
There is a further need, therefore, to have a process for fabricating a device or circuit having reduced loss that is compatible with existing fabrication processes. The process also preferably improves uniformity and repeatability of the fabricated devices or circuits.